1. Field of the Invention
The present invention relates to electro-optical color imaging apparatus and more specifically to such apparatus in which a plurality of discrete picture elements (pixels) of a color sensitive imaging layer(s) are concurrently imagewise exposed. The apparatus is highly useful for imaging with photoelectrophoretic dispersions but has application to many other color sensitive imaging layers, e.g., photographic emulsion layers.
2. Description of the Prior Art
Photoelectrophoretic migration imaging can be effected by the light image exposure of a dispersion layer, comprising photoconductive toner particles in a carrier medium, that is located between two electrodes providing a migration inducing field. U.S. Pat. No. 3,140,175 to Kaprelian discloses early procedures and apparatus of this type. In operation, the toner particles attain a charge and migrate from the dispersion to one of the electrodes. Upon exposure the illuminated particles migrate to the other electrode in accordance with the exposing light image pattern. Various embodiments for photoelectrophoretic migration imaging have been subsequently proposed (e.g., see U.S. Pat. No. 3,384,565). Recently a photoimmobilized electrophoretic migration imaging method has been described wherein the light-exposed, photoconductive toner particles are retained at the electrode to which they first migrate and unexposed particles change charge and migrate to the other electrode (see, e.g., U.S. Pat. No. 3,976,485).
Certain difficulties have arisen during efforts to commercialize such migration imaging systems; for example, high density images are difficult to attain. Also, for color imaging in general, it would be useful to have capabilities for color adjustment without inserting filter elements and image sense reversal without the forming of internegatives. Additionally, it is envisioned that office systems of the future may utilize electronic image transmission, and traditional optically-addressed copiers cannot accommodate such a future need.
In view of one or more of the problems and/or desired capabilities noted above, there have been described in the literature proposals for various electro-optical imaging systems. For example U.S. Pat. No. 3,663,396 and British Pat. No. 1,341,690 respectively disclose electronic address of a color cathode ray tube and an electro-luminescent panel used as the exposure source for a migration imaging system. Another electro-optical approach is disclosed in U.S. Pat. No. 4,058,828. In this device a multicolor laser beam is scanned point by point across the imaging area and modulated according to the point-by-point color content of the image to be reproduced. These approaches offer the potential for improved density, color adjustment and electronic transmission of images; however, the exposure elements and control systems for such systems are fairly complicated and expensive. The necessity to point scan an entire image also makes an imaging period somewhat lengthy.
My co-pending U.S. Application Ser. No. 821,114 entitled ELECTRONIC IMAGING USING MULTICOLOR ELECTROPHOTOSENSITIVE PARTICLES and filed Aug. 2, 1977 now U.S. Pat. No. 4,168,118 discloses an approach which has been found useful for obviating the above-described difficulties. In that approach, discrete pixels of migration imaging mixture are individually addressed by imagewise modulated electrical fields in timed relation to a series of differently colored light pulses. However in certain applications, difficulties have been encountered from the viewpoint of unwanted electrical interactions at the imaging zone and high voltage switching requirements.